1. Field of the Invention
This invention relates to an apparatus for compressively encoding an information signal including both a video signal and an audio signal.
2. Description of the Related Art
A prior-art information compressing apparatus in an MPEG (Moving Picture Experts Group) system compressively encodes a stream of original pictures each assigned to one of first, second, and third types. The first type corresponds to I-pictures (intra-coded pictures). The second type corresponds to P-pictures (predictive-coded pictures). The third type corresponds to B-pictures (bidirectionally predictive-coded pictures). The prior-art information compressing apparatus implements a compressing process GOP by GOP, where GOP means a group of pictures. Every GOP is composed of one I-picture and at least one P-picture or one B-picture. For every GOP, an I-picture is encoded first even in the case where the I-picture occupies a second or later picture place within the GOP.
As the numbers of original pictures in GOP""s increase, the qualities of encoding-resultant pictures rise. As the numbers of original pictures in GOP""s increase, units of the compressing process increase so that units of editing picture information also increase. The increased units make fine editing difficult. On the other hand, as the numbers of original pictures in GOP""s decrease, the qualities of encoding-resultant pictures drop.
It is assumed that editing causes encoding to pause at a P-picture in a GOP which follows an I-picture therein in the order of encoding. When encoding is restarted, it is necessary to commence encoding from the I-picture in that GOP again. Accordingly, in this case, the encoding of the I-picture is executed twice, and hence the efficiency of editing-related encoding work tends to be low.
In general, an original audio signal is also compressively encoded while the synchronization between audio information and video information is maintained. Audio information which results from editing tends to have a great stepwise level change at the editing point. Such a level change causes a click during the playback of the audio information.
It is an object of this invention to provide an information compressing apparatus capable of suppressing a click represented by a compression-resultant audio signal which might be caused by editing.
A first aspect of this invention provides an information compressing apparatus comprising a first address generation circuit for generating a first address signal; a second address generation circuit for generating a second address signal; a first memory for storing a video signal in response to the first address signal generated by the first address generation circuit; a second memory for storing an audio signal in response to the second address signal generated by the second address generation circuit; first means for periodically updating the first address signal generated by the first address generation circuit; second means for periodically updating the second address signal generated by the second address generation circuit; a first compression processing circuit for reading out the video signal from the first memory, and subjecting the read-out video signal to a first compressively encoding process; a second compression processing circuit for reading out the audio signal from the second memory, and subjecting the read-out audio signal to a second compressively encoding process; third means for detecting a head of every frame represented by the video signal; fourth means for storing a first state of the first address signal generated by the first address generation circuit which corresponds to a latest frame head detected by the third means; fifth means for storing a second state of the first address signal generated by the first address generation circuit which corresponds to a second frame head detected by the third means, the second frame head immediately preceding the latest frame head; sixth means for storing a first state of the second address signal generated by the second address generation circuit which corresponds to the latest frame head detected by the third means; seventh means for storing a second state of the second address signal generated by the second address generation circuit which corresponds to the second frame head detected by the third means; eighth means for detecting whether or not the video signal becomes discontinuous; ninth means for suspending operation of the first means and also operation of the first compression processing circuit when the eighth means detects that the video signal becomes discontinuous; tenth means for suspending operation of the second means and also operation of the second compression processing circuit when the eighth means detects that the video signal becomes discontinuous; eleventh means for detecting whether or not the video signal returns to a normally continuous state after the video signal becomes discontinuous; twelfth means for starting the updating of the first address signal by the first means from one of the first state stored by the fourth means and the second state stored by the fifth means when the eleventh means detects that the video signal returns to its normally continuous state after the video signal becomes discontinuous; thirteenth means for starting the updating of the second address signal by the second means from one of the first state stored by the sixth means and the second state stored by the seventh means when the eleventh means detects that the video signal returns to its normally continuous state after the video signal becomes discontinuous; and fourteenth means for, in cases where the eleventh means detects that the video signal returns to its normally continuous state after the video signal becomes discontinuous, reading out the audio signal from the second memory and mixing the read-out audio signal and a new audio signal into a mixing-resultant audio signal, and writing the mixing-resultant audio signal into the second memory until the second address signal reaches a prescribed address value.
A second aspect of this invention is based on the first aspect thereof, and provides an information compressing apparatus further comprising fifteenth means for deciding whether or not an address value represented by the second address signal, which occurs when the eighth means detects that the video signal becomes discontinuous, is smaller than the prescribed address value; sixteenth means for, in cases where the fifteenth means decides that the address value represented by the second address signal is smaller than the prescribed address value, to cause the twelfth means to start the updating of the first address signal from the second state stored by the fifth means; seventeenth means for, in cases where the fifteenth means decides that the address value represented by the second address signal is smaller than the prescribed address value, to cause the thirteenth means to start the updating of the second address signal from the second state stored by the seventh means; eighteenth means for, in cases where the fifteenth means decides that the address value represented by the second address signal is not smaller than the prescribed address value, to cause the twelfth means to start the updating of the first address signal from the first state stored by the fourth means; and nineteenth means for, in cases where the fifteenth means decides that the address value represented by the second address signal is not smaller than the prescribed address value, to cause the thirteenth means to start the updating of the second address signal from the first state stored by the sixth means.
A third aspect of this invention is based on the first aspect thereof, and provides an information compressing apparatus wherein the fourteenth means comprises means for fading in the new audio signal and fading out the read-out audio signal while mixing the read-out audio signal and the new audio signal.
A fourth aspect of this invention is based on the first aspect thereof, and provides an information compressing apparatus wherein the eighth means comprises an encoding pause button; and means for detecting whether or not the video signal becomes discontinuous in response to a position of the encoding pause button.
A fifth aspect of this invention is based on the first aspect thereof, and provides an information compressing apparatus wherein the eleventh means comprises an encoding pause button; and means for detecting whether or not the video signal returns to a normally continuous state after the video signal becomes discontinuous in response to a position of the encoding pause button.
A sixth aspect of this invention provides an apparatus comprising first means for detecting whether or not a first video signal becomes discontinuous and hence a defective frame picture occurs in a stream of frame pictures represented by the first video signal; second means for removing the defective frame picture from the stream of frame pictures to change the first video signal into a second video signal representing the stream of frame pictures except the defective frame picture; third means for dividing a first audio signal into a second audio signal and a third audio signal, the second audio signal occurring until the first video signal becomes discontinuous, the third audio signal occurring after the first video signal becomes discontinuous; fourth means for storing the second audio signal; and fifth means for mixing the second audio signal stored by the fourth means and the third audio signal into a fourth audio signal to fade in the third audio signal and to fade out the second audio signal in the fourth audio signal.